Goniometer head for x-ray diffraction apparatus with improved x- or y-motion mechanism

ABSTRACT

A goniometer head for securing and positioning a crystal specimen in X-ray diffraction apparatus-more particularly, an Xor Y-motion mechanism comprising a frame defining a channel within which is received a dovetailed carriage side-driven by a manually rotatable screw disposed parallel to and contiguous with the carriage. A carriage loading structure biases the screw transversely against the carriage and also functions to lock the carriage in the channel.

United States Patent Inventor Roy L. Thomas, Jr.

Medway, Mass.

Oct. 1, 1969 Dec. 21, 1971 Charles Supper Co., Inc. Natlclr, Mass.

Appl. No. Filed Patented Assignee GONIOMETER HEAD FOR X-RAY DIFFRAC'IION APPARATUS WITH IMPROVED X- 0R Y-MO'IION MECHANISM 3 Claims, 4 Drawing Figs.

US. Cl 248/184, 85/ 1 Int. Cl. ..Fl6m 11/12 Field of Search 248/184,

I85, I86, 183, I78, 179, 424, 298, 285; 269/60; 250/5 l .5; 74/441 [5 6] References Cited UNITED STATES PATENTS 1,211,895 1/1917 Theiss 248/133 2,913,241 11/1959 Miner 248/183 3,504,178 3/1970 Mariano 250/515 FOREIGN PATENTS 907,326 [0/1962 GreatBritain 250/515 Primary Examiner-Edward C. Allen Attorney-John H. Coult ABSTRACT: A goniometer head for securing and positioning a crystal specimen in X-ray diffraction apparatus-more par ticularly, an X- or Y-motion mechanism comprising a frame defining a channel within which is received a dovetailed carriage side-driven by a manually rotatable screw disposed parallel to and contiguous with the carriage. A carriage loading structure biases the screw transversely against the carriage and also functions to lock the carriage in the channel.

PATENTEUUEBZIB?! I 352 7 1 FIG.'3'

ROY L. THOMAS INVENTOR ATTORNEY GONIOMETER HEAD FOR X-RAY DIFFRACTION APPARATUS WITH IMPROVED X- OR Y-MOTION MECHANISM BACKGROUND OF THE INVENTION In Xray diffraction analysis of crystals, it is of utmost importance that the crystalographer be able to fix the position and orientation of the crystal specimen with maximum precision and accuracy and that the crystal, once positioned, remains in the set position with minimum position drift or play. Goniometer heads which have been developed for securing and positioning crystals commonly provide four degrees of crystal position adjustment, in addition to the azimuth adjustment capability usually incorporated in the goniometer head mount, namely, mutually orthogonal X- and Y-motions perpendicular to theaxis of the head (the Z-axis) and two orthogonal concentric arc motions. This invention concerns an improved X- or Y-(hereinafter X/Y) motion mechanism.

X/Y-motion mechanisms ideally should possess the following characteristics:

l. a positive, extremely precise adjustment action in either direction along its axis;

2. a capability of being locked securely in any position; and

3. an absence of any play or looseness during adjustment and after being locked.

Prior art X/Y-motion mechanisms have fallen considerably short of satisfying the above-defined ideal characteristics. Certain prior art X/Y-motion mechanisms comprise a carriage with dovetailed sides driven in a closely mating channel by a manually rotatable screw operating against a threaded concave cylindrical recess in the bottom of the carriage. To be tolerably free of play in the described remaining four degrees of freedom, such a mechanism must be machined to very close tolerances, and thus must be relatively costly to manufacture. Event the tightest tolerances, however, inherently and inevitably result in some unwanted play in the carriage.

Another type of prior art X/Y-motion mechanism comprises a floating carriage which is spring-biased in the direction of the Z-axis, thus minimizing Z-axis and arcuate play in the carriage. This arrangement results in some transverse and azimuthal play and is also relatively expensive to manufacture because of the tight machine tolerances required. t

I OBJECTS OF THE INVENTION It is an object of this invention to provide a goniometer head having X/Ymotion mechanisms which closely approach meeting the above-stated desirable characteristics. It is thus an object to provide X/Y-motion mechanisms which have a precise bidirectionally positive control, which exhibit very little transverse, arcuate, Z-axis, or azimuthal play, and which are fully lockable in any desired axial position.

It is another object to provide an X/Y-motion mechanism which is relatively inexpensive to manufacture.

Further objects and advantages of this invention will in part be obvious and will in part become apparent as the following description proceeds. The features of novelty which characterize the invention will be pointed out with particularity in the claims annexed to and forming a part of this specification.

BRIEF DESCRIPTION OF THE DRAWINGS For a fuller understanding of the invention, reference may be had to the following detailed description taken in connection with the accompanying drawings wherein:

FIG. 1 is a perspective view of a goniometer head having X- and Y-motion mechanisms embodying the principles of the invention;

FIG. 2 is a view of FIG. I with one of the X/Y-motion mechanisms exploded from the head;

FIG. 3 is a partial sectional view taken along lines 33 in FIG. l;and I FIG. 4 is a partial sectional view taken along lines 4-4 in FIG. 1.

DESCRIPTION OF THE PREFERRED EMBODIMENTS FIG. 1 illustrates a goniometer head including two line X- and Y-motion mechanisms embodying the principles of the invention. In the interest of conciseness, only one of the two mechanisms shown in FIG. 1, namely the Y-motion mechanism, will be illustrated and described in detail. In the illustrated goniometer head 10 an orthogonal pair of arc motion mechanisms are of conventional design. Outside arc motion mechanism 12 comprises an outside arc carriage 14 received in an outside arc channel member I6. Inside arc motion mechanism 18 comprises an inside are carriage 20 received in an inside arc channel member 22.

The FIG. 1 goniometer head also includes a crystal support 24 of conventional design, comprising a cylindrical collar 28 carried on the inside arc carriage 20. Collar 28 receives in a central bore a pin 30 upon which the crystal specimen 32 to be analyzed is mounted.

The X- and Y-motion mechanisms 34, 36, upon which the arc motion and Z-motion mechanisms ride, are constructed in accordance with the teachings of this invention and comprise, respectively, like carriages 40, 42 driven by adjustment screws 44, 66 and lockable by lock screws 48, 50. A frame 38 supporting the X- and Y-motion mechanisms 34, 36 is affixed to a base member (not shown) attached to a threaded cap 39 for securing the goniometer head 10 to a supporting structure therefor (not shown).

Refer now to FIG. 2 exploded view and the sectional views (FIGS. 3 and 4) which illustrate in detail the structure and operation of one of the like mechanisms, here shown to be the Y-motion mechanism 36. Frame 38 defines a channel 52, open at the top and ends, which receives the Y-motion carriage 42. One side 54 of the channel 52 is sloping and forms a female dovetail mating with a male dovetailed side 58 on carriage 42. The bottom 60 of the channel 52 is recessed, forming lips 61, 62 which support the carriage 42. As will be explained in more detail hereinafter, the dovetail configuration of the channel 52 and carriage 42 provides an extremely stable and precise support for the carriage, and assists in causing the carriage 42 to be self-locating and stabilizing in the channel 52.

The side 63 of the carriage 42 opposite side 58 is also sloping to form a dovetail, for reasons which will be pointed out below. The side 63 has formed thereon a series of regularly spaced grooves 64 which act as threads, the grooves 64 lying, respectively, in parallel planes perpendicular to the Y-axis. As will be seen, these grooves 64 mate with a helically grooved drive screw for the carriage 42. The fact that the grooves 64 lie in planes perpendicular to the Y-axis and thus are not helical allows the same pattern of grooves 64 to be driven by either a right or a left hand threaded screw. The area of peripheral overlap of the screw threads with the grooves 64 must be kept to a small fraction of the circumference of the drivescrew to prevent binding between the grooves 64 and the screw. The use of linear, nonhelical grooves or ridges in place of screw threads provides a substantial cost savings during manufacture of the head.

This point leads the discussion to another important feature of this inventionthe use of an adjustment means which is free to follow the carriage 42 transversely in the channel 52 as it seeks its stable position, and which assists in driving the carriage 42 to its stable position. In the illustrated embodiment, the adjustment means is disclosed as comprising a screw 66 having a helically threaded portion 68 and a manually accessible end 70 normally provided with a recessed socket suitable for precise rotatable adjustment by the operator.

The screw 66 is loosely received in the channel 52 adjacent the side 63 of the carriage 42 and oriented parallel to the carriage 42 and the Y-axis. The screw 66 is loosely captured in the channel 42 by the upper, lower and sidewalls, 74, 76, and 78 of the channel 52 and by the sides 63 of carriage 42. The screw 66 is restrained against longitudinal movement by a tongue 80 passing through a slit 82 in frame 38 where it is received in an annular groove 84 in screw 66. It is evident from the above description and FIGS. 2-4 that the screw 66 is free to move laterally in the channel 52, but is restricted against longitudinal play or motion. Thus, rotation of the screw 66 will be translated, through the screw threads and carriage grooves, into translational movement of the carriage 42.

It is a stated object of this invention to provide an X- or Y- motion mechanism having a very precise control and which is extremely stable and fully lockable in any desired position. Furthering this end, adjustable carriage loading means 86 are provided for placing a selectively variable compressive loading of the drive screw 66 against carriage 42. As will become evident, the carriage loading means 86 urges the carriage 42 laterally, causing the dovetailed carriage 42 and channel 52 to mate stabilize the carriage against play in the X-Y plane (except along the Y-axis), in arc, in azimuth, and along the Z- axis.

The carriage-loading means 86 is illustrated as comprising a manually adjustable carriage-loading screw 88 received in an internally threaded bore 90 in the frame 38. A pressure pad 92, which may be composed of Nylon or the like, is received in the bore 90 in engagement with the adjustment screw 66. A compression spring 94, located in the bore 90 between the carriage-loading screw 88 and the pressure pad 92, exerts a force on the pad 92 dependent on the axial position of the loading screw 88 in the bore 90. By manually rotating the loading screw 88, the operator can select the desired frictional force between the carriage 42 and the channel 52, and thus the amount of tightness or freedom from possible play of the carriage 42 as it travels in the channel 52.

The reason for the slope of side 63 of the carriage 42 to form a dovetail should now be readily understood. The pressure exerted on the carriage adjustment screw 66 by the carriage loading means 86 wedges the screw 66 between the upper wall 74 of the channel 42 and the side 63 of the carriage 42, forcing the carriage 42 downwardly into firm engagement with the lips 61, 62 defining the bottom supporting surface for the carriage 42 as it travels in the channel and enhancing the stability of the carriage in the channel 52.

To lock the carriage 42 in the channel 52, upon attaining the desired position of the crystal specimen 32 along the Y- axis, the loading screw 88 is rotated beyond a point wherein an extension 96 on the loading screw 88 engages the pad 92 directly and sufiicient force is exerted against the carriage 42 to frictionally lock the carriage 42 in the channel 52.

It is evident that this invention provides as X- or Y-motion mechanism which is extremely precise and free of play, which is fully lockable in any axial position, and which is relatively inexpensive to manufacture due to the low machine tolerances and other machining requirements.

The invention is not limited to the embodiment depicted which is merely illustrative. For example, whereas the illustrated carriage and channel arrangement may be described as a dovetail, other arrangements utilizing the dovetail principle may be employed in order that the carriage will be self-locating and self-stabilizing in its channel. The described mechanism may be adapted to provide crystal motion adjustment along the Z-axis as well as along the X- and Y-axes. it is thus contemplated that various and other modifications will occur to those skilled in the art.

What is claimed is:

1. In a goniometer head for X-ray diffraction apparatus having crystal position adjustment means providing two mutually orthogonal arcuate crystal motions, a mechanism for providing a translational crystal motion on an axis orthogonal to the longitudinal axis of the head, comprising:

carriage support means defining a channel oriented along said orthogonal axis, said channel having a bottom sur face and on one side a sloping side surface defining a female dovetail;

a carriage received in and slidable along said channel, said carriage having a sloping first side defining a male dovetail received in and mating with said female dovetail of said channel, and an opposite second side having a surface com onent slopin oppositely from first side, said carriage aving on sai second side threadlike means adapted to operatively engage a driving instrumentality;

screw means disposed loosely in said channel contiguous with and parallel to said second side of said carriage, said screw means having a manually accessible end and a threaded portion engaging said threadlike means on said second side of carriage for efi'ecting, upon rotation of said screw means, a translation of said carriage in said channel;

support means supporting said screw means loosely transverse to said orthogonal axis to allow rotation thereof but retaining said screw means against longitudinal movement; and

adjustable carriage-loading means for placing a variable compressive side loading on said screw means to urge said screw means against said surface component of said second side of said carriage and to thereby urge said male dovetail on said first side of said carriage into firm and stable engagement with said female dovetail on said chan nel.

2. The apparatus defined by claim I wherein said thrcadlike means on said carriage comprises grooves lying respectively in planes perpendicular to said orthogonal axis and engageable with a small fraction of the circumference of said threaded portion of said screw means.

3. The apparatus as defined by claim 2 wherein said adjustable carriage-loading means comprises means defining an internally threaded bore arranged transverse to said screw means, a carriage loading screw in said bore, a pressure pad aligned with said bore and engaging said screw means, and compression spring means in said bore between said carriage loading screw and said pad, rotation of said carriage loading screw causing an adjustment of the loading applied by said pad upon said screw means. 

1. In a goniometer head for X-ray diffraction apparatus having crystal position adjustment means providing two mutually orthogonal arcuate crystal motions, a mechanism for providing a translational crystal motion on an axis orthogonal to the longitudinal axis of the head, comprising: carriage support means defining a channel oriented along said orthogonal axis, said channel having a bottom surface and on one side a sloping side surface defining a female dovetail; a carriage received in and slidable along said channel, said carriage having a sloping first side defining a male dovetail received in and mating with said female dovetail of said channel, and an opposite second side having a surface component sloping oppositely from first side, said carriage having on said second side threadlike means adapted to operatively engage a driving instrumentality; screw means disposed loosely in said channel contiguous with and parallel to said second side of said carriage, said screw means having a manually accessible end and a threaded portion engaging said threadlike means on said second side of carriage for effecting, upon rotation of said screw means, a translation of said carriage in said channel; support means supporting said screw means loosely transverse to said orthogonal axis to allow rotation thereof but retaining said screw means against longitudinal movement; and adjustable carriage-loading means for placing a variable compressive side loading on said screw means to urge said screw means against said surface component of said second side of said carriage and to thereby urge said male dovetail on said first side of said carriage into firm and stable engagement with said female dovetail on said channel.
 2. The apparatus defined by claim 1 wherein said threadlike means on said carriage comprises grooves lying respectively in planes perpendicular to said orthogonal axis and engageable with a small fraction of the circumference of said threaded portion of said screw means.
 3. The apparatus as defined by claim 2 wherein said adjustable carriage-loading means comprises means defining an internally threaded bore arranged transverse to said screw means, a carriage loading screw in said bore, a pressure pad aligned with said bore and engaging said screw means, and compression spring means in said bore between said carriage loading screw and said pad, rotation of said carriage loading screw causing an adjustment of the loading applied by said pad upon said screw means. 